Parents get dating restraining orders?

I have heard many people SAY that they can get a restraining order to prevent a boy from dating their daughter but what is the actual law that permits this? In most states the requirements for an RO require someone engaging in violent or threatening or at least unlawful behavior.

Let's say a boy is 16, age of consent in Minnesota and his girlfriend is 18. Agreed that his parents can prevent her from visiting him in their home. But what provision of Minnesota law allows them to legally enforce a restraint on the woman in seeing or dating the boy?

They may have a parental right to order HIM not to see her and punish him or restrict him in some fashion, but if he goes to her of his own free will SHE is not interfering with their lawful custody or parental rights, is doing nothing illegal, and is not threatening anyone. So how can they get any kind of a restraining order against her?

Please reference a statute or case law, not personal opinions.